Such generic diaphragm valve is known from DE 101 53 362 B4. The attachment of the housing of the valve drive to the valve body is effected by a union nut which engages a lateral flange of the valve body and is rotatorily movable relative to the same and which engages into an external thread of a sleeve-like tab protruding from the valve body. The generic diaphragm valves to which the present invention relates do not employ a plurality of screws which extend through flanges at the valve body and at the housing in actuating direction of the valve drive, but there is employed a singular screw-nut connection which circumferentially and externally surrounds the diaphragm. As can be seen in DE 101 53 362 B4, the union nut is attached at the end of the valve drive facing away from the valve body and then is screwed on. The valve housing thereby is urged against the diaphragm, so that the diaphragm rim is axially clamped and tight between two ring-shaped bearing surfaces. The drive itself then engages the diaphragm via a tappet, in order to lift or lower said diaphragm, whereby the flow passage can be opened and closed. The valve body therefor has a valve seat. In a tubular valve body this valve seat usually is designed as at least one shut-off web which extends transversely to the flow passage and which together with the diaphragm, when the same rests against the same, shuts off the flow passage.
For the secure sealing and retention of the diaphragm it is important to clamp the same with a relatively closely predetermined contact pressure. A high frictional force occurs for example due to the dimensions of the threads and the contact surfaces between union nut and housing of the valve drive. Due to this high resistance it is relatively difficult to exactly achieve the desired optimum axial clamping force for the diaphragm during assembly or after a repair. In addition, it is disadvantageous to always have to design the union nut as large mounting part, because it must be attached across the valve drive. This also limits the lateral dimensions of the valve drive including housing, ports etc. The fact that the screw and the nut surround the diaphragm at its rim in actuating direction, more exactly in the region of the rim (i.e. along its rim), of course does not mean that the screw and the nut must be located at the height of the diaphragm as seen in a side view, as here the view in actuating direction is important.
It is the object of the invention to avoid the above disadvantages.